I saw this trick demonstrated by Scott Kelby in Lightroom 4, but it works equally well in Photoshop or LR3.
Sometimes it can be a bit tricky to find all of the sensor dust on your images, and then later on when you are doing some tonal manipulations you see some of the dust spots you miss become more pronounced. This will make it much easier for you to see the spots of dust in your images. As it turns out, my sensor is just perfect for demonstrating this as I haven’t cleaned it since returning from Namibia.
OK, Lets start by showing you a part of the image as it would appear normally. Click the image below to see it at full size and you will see some of the sensor spots immediately.
Now the trick is to add a curve adjustment layer and throw the curve into a pretty radical “sine wave” like the curve to the left. This will make your image look really funky and inverted, but have a look at what it does to the dust spots. To see the difference, click on the image below and feel sorry for how woefully dirty my sensor is.
What do you think? Cool?